This invention relates generally to method for manufacturing items and more particularly to a method and apparatus for molding such items out of a plurality of materials while optimizing the specific material utilization to achieve the desired structural and functional requirements.
One method of molding an object out of a polymer is an injection molding process. Injection molding comprises injecting a quantity of polymer in a melted state into a mold die which is contoured so that the resulting molded part has a particular desired shape. The melted polymer must be forced through an opening in the mold and the mold must be compressed at the same time so that the forcing of the melted polymer through the mold cavity does not force the mold open.
The more complex the tool the harder it is to push the polymer through the tool. Moreover, if the item requires materials of differing strengths and/or consistency those items generally are molded separately and are secured at a later point in the manufacturing process.
For example, and if the item is a structural beam for a vehicle other items such as knee energy absorbers which mold a part of the structural beam are often manufactured separately. These items are then joined to the structural beam separately by a suitable process, such as welding. Because multiple molds are used and multiple components must be joined, the above-described process is time consuming and costs are increased due to the presence of multiple steps.
The present invention utilizes the molding characteristics of an extrusion deposit compression molding process (EDCM), also known as extrusion compression molding, melt compression molding, or back compression molding, to mold an item.
EDCM is an open mold process, and this feature allows for the use of specific processing techniques to combine different polymer materials and/or inserts within the same tool or mold cavity.
According to the present invention an EDCM apparatus includes at least two separate deposition units each one having an extrusion die. Each deposition unit pushes a material through the die.
The EDCM apparatus also includes a compression mold which is molded of first and second mold dies which mate with one another so as to mold an item.
The apparatus is manipulated so that the extrusion die heads are passed over the mold to thereby deposit different materials into predetermined areas of the mold cavity. For example, a first material is deposited into the required sections of the mold cavity so as to mold one portion of an item. The second material is deposited in another section to mold another portion of the item.
The first and second materials have different characteristics and provide different features to the mold. It will be appreciated that the first material and the second material may be different thermoplastics of differing resiliency, strength, flexibility etc.
In addition, the open mold process allows the extrusion deposition unit to pass over the mold area regardless of its shape. Thus, the unit deposits the required molten material within the mold thereby reducing the required amount of flow of material to fill all of the cavities of the mold.
Furthermore, it will also be appreciated that the first material may contain an amount of reinforcing material and the second material may contain an amount of reinforcing material, wherein the amount and type of reinforcing material used in the first and second materials may be the same or they may be different.
The mold is closed and the deposited materials within the mold cavity fill out the mold cavity under pressure and the mold is opened after the required cooling time. The resultant molded article includes the different materials which mold the item.
The EDCM process provides a manufacturing cost reduction which is realized due to optimal material usage. Optimal material usage is accomplished by one or more of the following alternatives: (1) a lower cost material may be used for any specific area of the part due to the application of optimum reinforcement material and placement and use of the optimum material for each function and (2) the present invention provides the ability to mold thinner sections across the structural beam as may be justified by structural analysis. Additional cost savings are achieved through lower cost tooling and reduced tonnage equipment.
The EDCM process requires lower pressures as compared to other molding processes and accordingly results in a reduction in the tonnage of force and machinery required by the process. In addition, the EDCM process allows the use of more complex molds therefore the molded item will have fewer attached parts as they can be mold directly. By eliminating or using fewer attached parts, there is reduced opportunity for squeaks and rattles and other quality deficiencies to occur.
Other advantages of the present invention are discussed herein and include improved recyclability, a reduction in production costs, and ease of manufacture.
The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.